Imagine a dating site where, in addition to a completed survey, you have to submit a genetic profile. This could be the future of matchmaking, especially now that some scientists think that our compatibility genes—the same genes that determine whether an organ transplant will take—play a role in sexual attraction.

In a nutshell, can you explain the big idea—the thesis—of your new book, The Compatibility Gene?

The big idea is that a surprising amount of who and what we are comes from the way our species has evolved to survive disease. Put another way, this is about the idea that our immune system influences many aspects of human biology.

We each have a very similar set of genes—the 25,000 or so genes that make up the human genome—but there are variations that give us individual characteristics such as our hair or eye color. Crucially, the few human genes in this story—our compatibility genes—are those that vary the most from person to person. These genes are, in effect, a molecular mark that distinguishes each of us as individuals.

What role do compatibility genes play?

These genes are medically important because they influence the success of many types of medical transplants. These are the genes that doctors try to match in bone marrow transplantation, for example. And importantly, the versions of these genes that you have inherited influence which diseases you are susceptible or resistant to.

Other provocative research suggests that these very same genes also influence sexual attraction between two people, the wiring of our brains and the chance that a couple may have certain problems in pregnancy. We have no problem accepting that our physical characteristics—hair and eye color—are dictated by our genetic makeup. But can something that feels as intimate as choosing a partner be similarly influenced by our genetic inheritance? The subject is contentious, and there’s no simple answer. There is strong evidence that animals choose mates according to the versions of compatibility genes they have. There is evidence that something of this is true in humans, but the controversy is in establishing how big an effect this is—because human interactions are undoubtedly complex.

How did you get interested in this topic?

I took physics for my PhD because I thought that physical laws—constant across the whole Universe—had to be the most exciting, the most fundamental, stuff to study. As I got older, I became interested in life. I sort of stumbled into studying the immune system when I worked with a well-known immunologist, Jack Strominger, at Harvard University, after my PhD I’ve been studying the human immune system for over 15 years now.

What excites me about the immune system is that it’s an area of biology where a lot is not fully understood. It’s easy to hit the frontier. Why do some people get cancer or autoimmune diseases, and not others? In a database of 18 million people, there are four with compatibility genes similar to mine. And 6 percent of people in the 18 million are completely unique. However you view your place in the universe, some part of your individuality—your uniqueness—comes from the versions of these genes that you have inherited. So, studying immunology is, at this level, also a study of genetic differences between people.

What evidence do you have to support your idea?

This story has unraveled in a global adventure spanning 60 years, working out the science behind medical transplants and immunology, leading to our eventual understanding of how and why compatibility genes are crucial to our health. This is a revolution in our understanding of the human body, but not one that came in a single Eureka moment; this knowledge has come from experiments happening in different places across the globe over decades.

Every big thinker has predecessors to whom he is indebted. Who laid the foundation for you to build your idea? Who is your hero?

My book begins with Peter Medawar who, working in Oxford in the early 1950s, carried out several groundbreaking experiments, which won him a Nobel Prize, alongside Australian [Sir Frank] Macfarlane Burnet.

Seeing the agony of airmen suffering from drastic skin burns at a War Wounds Hospital in Oxford in 1940 focused Medawar’s mind on solving the difficulties that surgeons had in getting skin transplantation to work. His research went on to establish that the difficulties in medical transplantation were caused by a reaction from the recipient’s immune cells. This, together with theoretical ideas developed by Burnet, helped establish basic principles about how our immune system works.

In essence, they realized that the immune system recognizes and destroys substances that are not part of you—germs or transplanted organs. This implied that transplantation was not just about getting the surgery right. Up until this time, most surgeons thought if they could perform a technically perfect graft, the transplantation would work. But this was wrong; there was a fundamental barrier of an immune reaction to be overcome in order for skin grafts between genetically different people to work, because transplanted cells or tissues are detected as not being part of you. Genetic matching between people and the use of immune suppressive drugs make clinical transplantation work today, and both directly build upon Medawar and Burnet’s insights.

What is new about your thinking?

At one level, this is a story about six decades of research—and not a single recent breakthrough experiment. But through putting it all together, a new and fascinating theme emerges; that there are far-reaching consequences from the way our body fights disease. Not least is that this knowledge gives a new view of why our own uniqueness is fundamentally crucial.

For the way our body fights disease, it is beneficial to keep these genes exceptionally diverse. It would be no good if one sweeping infectious disease that killed people with certain versions of these genes would simply narrow the variation in these genes that got passed on to the next generation and lower our chances against other diseases in the future. This science has a powerful message for society: Nobody has a perfect set of compatibility genes. It’s our great genetic diversity that’s essential.

What two or three people are most likely to try to refute your argument? Why?

As I said, controversial experiments indicate that these immune system genes can also play a role influencing sexual attraction between people and the likelihood of couples having particular problems in pregnancy. One experiment in this line of thinking used a very unusual protocol for scientific work. Women were to refrain from sex for two days, use a nasal spray to keep their nostrils clear, read Patrick Süskind’s novel Perfume—about a man with olfactory hypersensitivity who is obsessed with people’s smells—and then come into the lab to smell a collection of T-shirts worn by men who hadn’t showered for two days. The experiment yielded the astonishing result that T-shirts worn by people with different compatibility genes smelt the sexiest. This seems to indicate that we subconsciously prefer sexual partners who have different compatibility genes from ourselves.

One problem is that it’s hard to know if any difference in smell detected here would actually influence a person’s behavior. There is strong evidence of this in animals, but for humans, relationships are more complex. Scientists differ in their views on this.

Who will be most affected by this idea?

This book gives new insight into how the human body works, and makes the link between immunity and attraction. So, just like learning about the idea of evolution itself, my hope is that one's life is simply enriched by these basic insights into human behavior: “Wow, so this is how it works.” I hope to get across a new view as to why we are each special on a molecular level and that there is a fundamental importance to our uniqueness.

How might it change life, as we know it?

On a practical level, readers can get genetic tests to know about the diseases they are susceptible or resistant to, or to know who they may be compatible with for partnerships or pregnancy. Such decisions are personal, and I'm not directly advising anyone what to do, rather my book explains all these ideas in depth, so that each person can make an informed decision. Just one example: Given that we each respond slightly differently to any particular disease, it can be expected that we also respond slightly differently to any given medicine. In the near future, the choice of drugs we are given for treatments may well be tailored to match our genes. Already now, there is evidence that the side effects of some drugs can be avoided if people with certain genes are not given those drugs.

What questions are left unanswered?

The urgent debate, in universities and pharmaceutical companies alike, is in how to get the best out of the knowledge we’ve accumulated. How do we translate revelations in our understanding of genetics and disease into actual medical benefit?